Gratuity

I am throwing a bridal shower at a restaurant where they do not split the check, and they add 20% gratuity to the check? I along with a few others are paying for appetizers and we're providing dessert; the guests are responsible for their meals. Now the gratuity-who's responsible for that? I personally do not believe that I would have enough to cover that on my own? Any suggestions anyone?

 

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